Thermodynamic Modeling the Solid–Liquid Phase Equilibrium of a Water–Methanol–Potassium Dihydrogen Phosphate Ternary System with a Mixed-Solvent Electrolyte (MSE) Model

Abstract

The solubility measurement of potassium dihydrogen phosphate (MKP) in a water–methanol system is of great significance for the salting-out crystallization of MKP. The solubility of MKP in the H2O–CH3OH solution was determined by the static equilibrium method in the range of 283.15–343.15 K, and the molar fraction of CH3OH varied from 0.0588 to 0.6923. The mixed-solvent electrolyte model (MSE) was used to regress the experimental results, and new parameters were obtained. Based on it, the thermodynamic model of the H2O–CH3OH–MKP system was established, which is in good agreement with the experimental results, with a relative average absolute deviation of 6.46%. Then, the change in the ion concentration and the activity coefficients in the system were predicted by the thermodynamic model. Finally, the Pixact Crystallization Monitoring (PCM) system and a scanning electron microscope (SEM) were used to observe the crystallization process and the morphology of MKP in the H2O–CH3OH system, respectively.